Record Details
Structure and neotectonics of the northwestern Nanga Parbat-Haramosh massif
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | Structure and neotectonics of the northwestern Nanga Parbat-Haramosh massif |
| Names |
Madin, Ian P.
(creator) Lawrence, Robert D. (advisor) |
| Date Issued | 1986-05-29 (iso8601) |
| Note | Graduation date: 1987 |
| Abstract | The Nanga Parbat-Haramosh massif (NPHM) is a unique structural and topographic high in the northwestern corner of the Himalayan convergence zone. Previously, the NPHM was thought to be bounded by the MMT, a thrust along which the Kohistan-Ladakh island arc was obducted onto the northern margin of fridia. This study presents field evidence for the existence of the Raikot fault, an active dextral reverse fault which has truncated the MMT and forms the western boundary of the NPHM. The Raikot fault separates medium-grade Mesozoic to mid-Cenozoic mafic metasediments and intrusive rocks of the Kohistan sequence from high-grade Proterozoic metasediments and orthogneiss of the Nanga Parbat group. The Kohistan sequence rocks have experienced one tight to isoclinal folding event probably associated with the obduction of the island arc, and a second folding event associated with movement on the Raikot fault. The Nanga Parbat group rocks were transposed by a pre-Himalayan isoclinal folding event and have subsequently been folded around east-trending axes in the early Cenozoic by the obduction of Kohistan, then around north-trending axes in the late Cenozoic, associated with the uplift of the NPHM and the initiation of the Raikot fault. The Raikot fault consists of both mylonite zones and numerous major and minor faults. Slickensides and mylonitic lineations both indicate dextral reverse slip. The Raikot fault and associated folding appear to have accommodated 15 to 25 km of uplift in the late Cenozoic. The concentration of the uplift and involvement of the Moho suggests that the Raikot fault follows a major crustal structure, possibly a pre-collision Indian plate boundary. If this is the case, rotational underthrusting of greater India along the MMT would require dextral slip along the Raikot fault. It is proposed that the Raikot fault is a terminal tear fault on the MCT. Four ages of glaciation are recognized in the area, and correlated with regional glacial chronologies. Numerous Holocene offsets of glacial deposits and alluvial fans occur. A till surface attributed to the most recent major advance has been offset approximately 160 m vertically by strands of the Raikot fault. Analysis of the offsets in combination with thermoluminessence dating yield a maximum Holocene uplift rate of 3.9 mm /yr. This uplift rate is compatible with published values derived from fission-track cooling rates. |
| Genre | Thesis/Dissertation |
| Topic | Geology -- India -- Nanga Parbat Region |
| Identifier | http://hdl.handle.net/1957/40289 |
